In mining and construction environments, heavy-duty off-highway trucks are used to haul a variety of materials such as, for example, coal, rock, ore, and overburden materials. Such heavy-duty off-highway trucks generally comprise a truck chassis or frame which supports a dump body for receiving and carrying a load. In order to ensure that the dump body is properly balanced, the dump body should be designed based on an anticipated load distribution of the material carried on the truck chassis or frame. More specifically, the truck chassis anticipates a particular optimal location on the chassis where the center of gravity of the load carried in the dump body should be positioned.
Trucks with dump bodies which are often sold by the original equipment manufacturers have dump bodies designed around an assumed load configuration or load profile. In designing these dump bodies, however, the load profile which is used to size the body is based on a theoretical material angle of repose or load heap of the material irrespective of material cohesiveness, individual material heaping characteristics or material gradation. For example, in designing a dump body for hauling coal one theoretical material heap which is often used is a 3:1 heap (corresponding to an angle of repose of approximately 18°). With bodies designed to haul overburden, a theoretical material heap of 2:1 (or a different S.A.E. 2:1 heap) is often assumed.
Historically, off-highway truck manufacturers have been unable to reach a consensus with regards to the theoretical load heaps or configurations, let alone any consensus on the individual hauled material characteristics that should be used to design the dump bodies. As evidenced by their commercially available literature, some off-highway truck manufacturers use theoretical material heap profiles based on standards promulgated by the Society of Automotive Engineers (S.A.E. J 1363 January 1985) while others use their own heap profiles. Moreover, many off-highway truck manufacturers have over time alternated between using various different theoretical load heap profiles or configurations to design their dump bodies.
Off-highway truck manufacturers use these theoretical load heap profiles so that they are able to mass produce their dump bodies. However, the theoretical load heap, and the resulting theoretical load profiles, which the truck manufacturers use to design their dump bodies ignore a number of factors. For example, theoretical load profiles do not take into account the particular material characteristics of the material being loaded and hauled. In addition, theoretical load profiles do not take into account the corner voids which occur when a load is placed in the dump body. In particular, since the material is loaded from overhead into the dump body, the material tends to try to form a generally conical shape in the dump body. Because the load conforms to a generally conical shape, voids are created in the corners of the dump body where no material is present. The theoretical load profiles as used by truck manufacturers ignore these corner voids.
Additionally, field loading/haulage conditions impact the actual angles of repose that the loaded material forms in the dump body. In the loading process, material on its own flows to a natural angle of repose, however, in the loading process as the loading equipment pushes/pulls and rests on the material being loaded an imposed material angle of repose results. For instance, the method by which the material is actually loaded into the dump body, e.g. using a front-end loader or a shovel, can impact the ultimate actual profile of the load in the body. Other material characteristics such as the cohesiveness, gradation, size and consistency of the material (e.g., ore, overburden, clay, etc.) also impacts the actual load profile. Accordingly, because of differences in the materials and field loading and haulage conditions, the actual load profile or configuration of given materials in the dump body at different sites can vary extensively.
As a result, the mass-produced dump bodies supplied by off-highway truck manufacturers which are based on a theoretical material load profile are often improperly matched for a particular material haulage application. For example, the dump body may be inadvertently designed such that the dump body size and resultant load is either undersized/underloaded or oversized/overloaded and that the corresponding center of gravity of the actual load is significantly offset from where it should be placed, based on the design of the truck chassis. This causes incorrect truck loading and improper truck utilization with uneven loading of the truck chassis leading to uneven or offset frame loading, which can potentially result in truck chassis problems including uneven tire wear which often requires premature replacement of the tires; and potentially poor vehicle operating stability. As will be appreciated, since the trucks themselves and the tires used on these types of off-highway trucks are extremely costly, potential truck chassis repair and premature replacement of tires significantly increases the operating expenses associated with material haulage.
Likewise, depending on how the actual material and material heap varies from a theoretical material load profile, the dump body can be either too large or too small resulting in the truck chassis carrying loads which are both improperly placed on the truck frame and significantly heavier or lighter than intended. An improperly designed body which is too small to carry the intended load can lead to spillage of the load over the sides and off the rear end of the body resulting in significant under utilization of the truck. If side/rear spillage occurs during transport, it can result in tire damage and tire ruptures particularly on the following trucks. While too large of a body for the intended load can result in extreme truck overloads or if the load is limited to the correct load amount in the dump body, the load may often be improperly placed in the dump body leading to poor truck stability and individual truck chassis component overloads.